Phosphors comprising silicates, phosphates (for example, apatite) and aluminates as host materials, with transition metals or rare earth metals added as activating materials to the host materials, are widely known. As blue LEDs, in particular, have become practical in recent years, the development of white light sources utilizing such blue LEDs in combination with such phosphor materials is being energetically pursued.
Especially red emitting luminescent materials have been in the focus of interest and several materials have been proposed, e.g. U.S. Pat. No. 6,680,569(B2), “ Red Deficiency Compensating Phosphor for a Light Emitting Device”, or from WO patent application 2005/052087 A1.
However, there is still the continuing need for orange to red emitting luminescent materials which are usable within a wide range of applications and especially allow the fabrication of phosphor warm white pcLEDs with optimized luminous efficiency and color rendering.